Methods and apparatus for effectuating a lasting change in a neural-function of a patient

ABSTRACT

The following disclosure describes several methods and apparatus for intracranial electrical stimulation to treat or otherwise effectuate a change in neural-functions of a patient. Several embodiments of methods in accordance with the invention are directed toward enhancing or otherwise inducing a lasting change in neural activity to effectuate a particular neural-function. Such lasting change in neural activity is defined as “neuroplasticity.” The methods in accordance with the invention can be used to treat brain damage (e.g., stroke, trauma, etc.), brain disease (e.g., Alzheimer&#39;s, Pick&#39;s, Parkinson&#39;s, etc.), and/or brain disorders (e.g., epilepsy, depression, etc.). The methods in accordance with the invention can also be used to enhance neural-function of normal, healthy brains (e.g., learning, memory, etc.), or to control sensory functions (e.g., pain). Certain embodiments of methods in accordance with the invention electrically stimulate the brain at a stimulation site where neuroplasticity is occurring. The stimulation site may be different than the region in the brain where neural activity is typically present to perform the particular neural function according to the functional organization of the brain. In one embodiment in which neuroplasticity related to the neural-function occurs in the brain, the method can include identifying the location where such neuroplasticity is present. In an alternative embodiment in which neuroplasticity is not occurring in the brain, an alternative aspect is to induce neuroplasticity at a stimulation site where it is expected to occur. Several embodiments of these methods that are expected to produce a lasting effect on the intended neural activity at the stimulation site use electrical pulses that increase the resting membrane potential of neurons at the stimulation site to a subthreshold level.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/217,981, filed Jul. 31, 2000, which is incorporated herein in itsentirety.

TECHNICAL FIELD

Several embodiments of methods and apparatus in accordance with theinvention are related to electrically stimulating a region in the cortexor other area of the brain to bring about a lasting change in aphysiological function and/or a mental process of a patient.

BACKGROUND

A wide variety of mental and physical processes are known to becontrolled or are influenced by neural activity in particular regions ofthe brain. In some areas of the brain, such as in the sensory or motorcortices, the organization of the brain resembles a map of the humanbody; this is referred to as the “somatotopic organization of thebrain.” There are several other areas of the brain that appear to havedistinct functions that are located in specific regions of the brain inmost individuals. For example, areas of the occipital lobes relate tovision, regions of the left inferior frontal lobes relate to language inthe majority of people, and regions of the cerebral cortex appear to beconsistently involved with conscious awareness, memory, and intellect.This type of location-specific functional organization of the brain, inwhich discrete locations of the brain are statistically likely tocontrol particular mental or physical functions in normal individuals,is herein referred to as the “functional organization of the brain.”

Many problems or abnormalities with body functions can be caused bydamage, disease and/or disorders of the brain. A stroke, for example, isone very common condition that damages the brain. Strokes are generallycaused by emboli (e.g., obstruction of a vessel), hemorrhages (e.g.,rupture of a vessel), or thrombi (e.g., clotting) in the vascular systemof a specific region of the cortex, which in turn generally causes aloss or impairment of a neural function (e.g., neural functions relatedto face muscles, limbs, speech, etc.). Stroke patients are typicallytreated using physical therapy to rehabilitate the loss of function of alimb or another affected body part. For most patients, little can bedone to improve the function of the affected limb beyond the recoverythat occurs naturally without intervention. One existing physicaltherapy technique for treating stroke patients constrains or restrainsthe use of a working body part of the patient to force the patient touse the affected body part. For example, the loss of use of a limb istreated by restraining the other limb. Although this type of physicaltherapy has shown some experimental efficacy, it is expensive,time-consuming and little-used. Stroke patients can also be treatedusing physical therapy plus adjunctive therapies. For example, sometypes of drugs, such as amphetamines, that increase the activation ofneurons in general, appear to enhance neural networks; these drugs,however, have limited efficacy because they are very non-selective intheir mechanisms of action and cannot be delivered in highconcentrations directly at the site where they are needed. Therefore,there is a need to develop effective treatments for rehabilitatingstroke patients and patients that have other types of brain damage.

Other brain disorders and diseases are also difficult to treat.Alzheimer's disease, for example, is known to affect portions of thecortex, but the cause of Alzheimer's disease and how it alters theneural activity in the cortex is not fully understood. Similarly, theneural activity of brain disorders (e.g., depression andobsessive-compulsive behavior) is also not fully understood. Therefore,there is also a need to develop more effective treatments for otherbrain disorders and diseases.

The neural activity in the brain can be influenced by electrical energythat is supplied from an external source outside of the body. Variousneural functions can thus be promoted or disrupted by applying anelectrical current to the cortex or other region of the brain. As aresult, the quest for treating damage, disease and disorders in thebrain have led to research directed toward using electricity ormagnetism to control brain functions.

One type of treatment is transcranial electrical stimulation (TES),which involves placing an electrode on the exterior of the scalp anddelivering an electrical current to the brain through the scalp andskull. Patents directed to TES include: U.S. Pat. No. 5,540,736 issuedto Haimovich et al. (for providing analgesia); U.S. Pat. No. 4,140,133issued to Katrubin et al. (for providing anesthesia); U.S. Pat. No.4,646,744 issued to Capel (for treating drug addiction, appetitedisorders, stress, insomnia and pain); and U.S. Pat. No. 4,844,075issued to Liss et al. (for treating pain and motor dysfunctionassociated with cerebral palsy). TES, however, is not widely usedbecause the patients experience a great amount of pain and theelectrical field is difficult to direct or focus accurately.

Another type of treatment is transcranial magnetic stimulation (TMS),which involves producing a high-powered magnetic field adjacent to theexterior of the scalp over an area of the cortex. TMS does not cause thepainful side effects of TES. Since 1985, TMS has been used primarily forresearch purposes in brain-mapping endeavors. Recently, however,potential therapeutic applications have been proposed primarily for thetreatment of depression. A small number of clinical trials have foundTMS to be effective in treating depression when used to stimulate theleft prefrontal cortex.

The TMS treatment of a few other patient groups have been studied withpromising results, such as patients with Parkinson's disease andhereditary spinocerebellar degeneration. Patents and published patentapplications directed to TMS include: published international patentapplication WO 98/06342 (describing a transcranial magnetic stimulatorand its use in brain mapping studies and in treating depression); U.S.Pat. No. 5,885,976 issued to Sandyk (describing the use of transcranialmagnetic stimulation to treat a variety of disorders allegedly relatedto deficient serotonin neurotransmission and impaired pineal melatoninfunctions); and U.S. Pat. No. 5,092,835 issued to Schurig et al.(describing the treatment of neurological disorders (such as autism),treatment of learning disabilities, and augmentation of mental andphysical abilities of “normal” people by a combination of transcranialmagnetic stimulation and peripheral electrical stimulation).

Independent studies have also demonstrated that TMS is able to produce alasting change in neural activity within the cortex that occurs for aperiod of time after terminating the TMS treatment (“neuroplasticity”).For example, Ziemann et al., Modulation of Plasticity in Human MotorCortex after Forearm Ischemic Nerve Block, 18 J Neuroscience 1115(February 1998), disclose that TMS at subthreshold levels (e.g., levelsat which movement was not induced) in neuro-block models that mimicamputation was able to modify the lasting changes in neural activitythat normally accompany amputation. Similarly, Pascual-Leone et al.(submitted for publication) disclose that applying TMS over thecontralateral motor cortex in normal subjects who underwentimmobilization of a hand in a cast for 5 days can prevent the decreasedmotor cortex excitability normally associated with immobilization. Otherresearchers have proposed that the ability of TMS to produce desiredchanges in the cortex may someday be harnessed to enhanceneuro-rehabilitation after a brain injury, such as stroke, but there areno published studies to date.

Other publications related to TMS include Cohen et al., Studies ofNeuroplasticity With Transcranial Magnetic Stimulation, 15 J. Clin.Neurophysiol. 305 (1998); Pascual-Leone et al., Transcranial MagneticStimulation and Neuroplasticity, 37 Neuropsychologia 207 (1999); Stefanet al., Induction of Plasticity in the Human Motor Cortex by PairedAssociative Stimulation, 123 Brain 572 (2000); Sievner et al., LastingCortical Activation after repetitive TMS of the Motor Cortex, 54Neurology 956 (February 2000); Pascual-Leone et al., Study andModulation of Human Cortical Excitability With Transcranial MagneticStimulation, 15 J. Clin. Neurophysiol. 333 (1998); and Boylan et al.,Magnetoelectric Brain Stimulation in the Assessment Of Brain PhysiologyAnd Pathophysiology, 111 Clin. Neurophysiology 504 (2000).

Although TMS appears to be able to produce a change in the underlyingcortex beyond the time of actual stimulation, TMS is not presentlyeffective for treating many patients because the existing deliverysystems are not practical for applying stimulation over an adequateperiod of time. TMS systems, for example, are relatively complex andrequire stimulation treatments to be performed by a healthcareprofessional in a hospital or physician's office. TMS systems also maynot be reliable for longer-term therapies because it is difficult to (a)accurately localize the region of stimulation in a reproducible manner,and (b) hold the device in the correct position over the cranium for along period, especially when a patient moves or during rehabilitation.Furthermore, current TMS systems generally do not sufficiently focus theelectromagnetic energy on the desired region of the cortex for manyapplications. As such, the potential therapeutic benefit of TMS usingexisting equipment is relatively limited.

Direct and indirect electrical stimulation of the central nervous systemhas also been proposed to treat a variety of disorders and conditions.For example, U.S. Pat. No. 5,938,688 issued to Schiff notes that thephenomenon of neuroplasticity may be harnessed and enhanced to treatcognitive disorders related to brain injuries caused by trauma orstroke. Schiff's implant is designed to increase the level of arousal ofa comatose patient by stimulating deep brain centers involved inconsciousness. To do this, Schiff's invention involves electricallystimulating at least a portion of the patient's intralaminar nuclei(i.e., the deep brain) using, e.g., an implantable multipolar electrodeand either an implantable pulse generator or an external radiofrequencycontrolled pulse generator. Schiff's deep brain implant is highlyinvasive, however, and could involve serious complications for thepatient.

Likewise, U.S. Pat. No. 6,066,163 issued to John acknowledges theability of the brain to overcome some of the results of an injurythrough neuroplasticity. John also cites a series of articles asevidence that direct electrical stimulation of the brain can reverse theeffects of a traumatic injury or stroke on the level of consciousness.The system disclosed in John stimulates the patient and modifies theparameters of stimulation based upon the outcome of comparing thepatient's present state with a reference state in an effort to optimizethe results. Like Schiff, however, the invention disclosed in John isdirected to a highly invasive deep brain stimulation system.

Another device for stimulating a region of the brain is disclosed byKing in U.S. Pat. No. 5,713,922. King discloses a device for corticalsurface stimulation having electrodes mounted on a paddle implantedunder the skull of the patient. The electrodes are implanted on thesurface of the brain in a fixed position. The electrodes in Kingaccordingly cannot move to accommodate changes in the shape of thebrain. King also discloses that the electrical pulses are generated by apulse generator that is implanted in the patient remotely from thecranium (e.g., subclavicular implantation). The pulse generator is notdirectly connected to the electrodes, but rather it is electricallycoupled to the electrodes by a cable that extends from the remotelyimplanted pulse generator to the electrodes implanted in the cranium.The cable disclosed in King extends from the paddle, around the skull,and down the neck to the subclavicular location of the pulse generator.

King discloses implanting the electrodes in contact with the surface ofthe cortex to create paresthesia, which is a sensation of vibration or“buzzing” in a patient. More specifically, King discloses inducingparesthesia in large areas by applying electrical stimulation to ahigher element of the central nervous system (e.g., the cortex). Assuch, King discloses placing the electrodes against particular regionsof the brain to induce the desired paresthesia. The purpose of creatingparesthesia over a body region is to create a distracting stimulus thateffectively reduces perception of pain in the body region. Thus, Kingappears to require stimulation above activation levels.

Although King discloses a device that stimulates a region on thecortical surface, this device is expected to have several drawbacks.First, it is expensive and time-consuming to implant the pulse generatorand the cable in the patient. Second, it appears that the electrodes areheld at a fixed elevation that does not compensate for anatomicalchanges in the shape of the brain relative to the skull, which makes itdifficult to accurately apply an electrical stimulation to a desiredtarget site of the cortex in a focused, specific manner. Third, Kingdiscloses directly activating the neurons to cause paresthesia, which isnot expected to cause entrainment of the activity in the stimulatedpopulation of neurons with other forms of therapy or adaptive behavior,such as physical or occupational therapy. Thus, King is expected to haveseveral drawbacks.

King and the other foregoing references are also expected to havedrawbacks in producing the desired neural activity because thesereferences generally apply the therapy to the region of the brain thatis responsible for the physiological function or mental processaccording to the functional organization of the brain. In the case of abrain injury or disease, however, the region of the brain associatedwith the affected physiological function or cognitive process may notrespond to stimulation therapies. Thus, existing techniques may notproduce adequate results that last beyond the stimulation period.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic view of neurons.

FIG. 1B is a graph illustrating firing an “action potential” associatedwith normal neural activity.

FIG. 1C is a flowchart of a method for effectuating a neural-function ofa patient associated with a location in the brain in accordance with oneembodiment of the invention.

FIG. 2 is a top plan view of a portion of a brain illustrating neuralactivity in a first region of the brain associated with theneural-function of the patient according to the somatotopic organizationof the brain.

FIG. 3 is a top plan image of a portion of the brain illustrating a lossof neural activity associated with the neural-function of the patientused in one stage of a method in accordance with an embodiment of theinvention.

FIG. 4 is a top plan image of the brain of FIG. 3 showing a change inlocation of the neural activity associated with the neural-function ofthe patient at another stage of a method in accordance with anembodiment of the invention.

FIGS. 5A and 5B are schematic illustrations of an implanting procedureat a stage of a method in accordance with an embodiment of theinvention.

FIG. 5C is a graph illustrating firing an “action potential” associatedwith stimulated neural activity in accordance with one embodiment of theinvention.

FIG. 6 is an isometric view of an implantable stimulation apparatus inaccordance with one embodiment of the invention.

FIG. 7 is a cross-sectional view schematically illustrating a part of animplantable stimulation apparatus in accordance with an embodiment ofthe invention.

FIG. 8 is a schematic illustration of a pulse system in accordance withone embodiment of the invention.

FIG. 9 is a schematic illustration of an implanted stimulation apparatusand an external controller in accordance with an embodiment of theinvention.

FIG. 10 is a schematic illustration of an implantable stimulationapparatus having a pulse system and an external controller in accordancewith another embodiment of the invention.

FIG. 11 is a cross-sectional view schematically illustrating a part ofan implantable stimulation apparatus in accordance with an embodiment ofthe invention.

FIG. 12 is a schematic illustration of an implantable stimulationapparatus having a pulse system and an external controller in accordancewith another embodiment of the invention.

FIG. 13 is a cross-sectional view schematically illustrating a part ofan implantable stimulation apparatus having a pulse system and anexternal controller in accordance with another embodiment of theinvention.

FIG. 14 is a bottom plan view and FIG. 15 is a cross-sectional viewillustrating an electrode configuration for an implantable stimulationapparatus in accordance with an embodiment of the invention.

FIG. 16 is a bottom plan view and FIG. 17 is a cross-sectional view ofan electrode configuration for an implantable stimulation apparatus inaccordance with another embodiment of the invention.

FIG. 18 is a bottom plan view and FIG. 19 is a cross-sectional view ofan electrode configuration in accordance with yet another embodiment ofthe invention.

FIG. 20 is a bottom plan view of an electrode configuration for animplantable stimulation device in accordance with yet another embodimentof the invention.

FIG. 21 is a bottom plan view of an electrode configuration for animplantable stimulation device in accordance with another embodiment ofthe invention.

FIG. 22 is a bottom plan view of yet another embodiment of an electrodeconfiguration for use with an implantable stimulation apparatus inaccordance with the invention.

FIG. 23 is a bottom plan view and FIG. 24 is a cross-sectional view ofan electrode configuration for use with a stimulation apparatus inaccordance with still another embodiment of the invention.

FIG. 25 is an isometric view schematically illustrating a part of animplantable stimulation apparatus with a mechanical biasing element inaccordance with an embodiment of the invention.

FIG. 26 is a cross-sectional view of a stimulation apparatus having amechanical biasing element that has been implanted into a skull of apatient in accordance with an embodiment of the invention.

FIG. 27 is a cross-sectional view schematically illustrating a part of astimulation apparatus having a biasing element in accordance with anembodiment of the invention.

FIG. 28 is a cross-sectional view of a stimulation apparatus having abiasing element in accordance with still another embodiment of theinvention.

FIG. 29 is a cross-sectional view of a stimulation apparatus having abiasing element in accordance with yet another embodiment of theinvention.

FIG. 30 is a cross-sectional view of a stimulation apparatus having abiasing element in accordance with yet another embodiment of theinvention.

FIG. 31 is a cross-sectional view schematically illustrating a portionof an implantable stimulation apparatus having an external power sourceand pulse generator in accordance with an embodiment of the invention.

FIG. 32 is a cross-sectional view schematically illustrating a portionof an implantable stimulation apparatus having an external power sourceand pulse generator in accordance with another embodiment of theinvention.

FIG. 33 is a cross-sectional view illustrating in greater detail aportion of the implantable stimulation apparatus of FIG. 32.

FIG. 34 is a cross-sectional view schematically illustrating a portionof an implantable stimulation apparatus and an external controller inaccordance with another embodiment of the invention.

FIG. 35 is a cross-sectional view schematically illustrating a portionof an implantable stimulation apparatus and an external controller inaccordance with yet another embodiment of the invention.

FIG. 36 is a cross-sectional view schematically illustrating a portionof an implantable stimulation apparatus in accordance with yet anotherembodiment of the invention.

FIG. 37 is an isometric view and FIG. 38 is a cross-sectional viewillustrating an implantable stimulation apparatus in accordance with anembodiment of the invention.

FIG. 39 is a cross-sectional view illustrating an implantablestimulation apparatus in accordance with yet another embodiment of theinvention.

FIG. 40 is a schematic illustration of an implantable stimulationapparatus in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

The following disclosure describes several methods and apparatus forintracranial electrical stimulation to treat or otherwise effectuate achange in neural-functions of a patient. Several embodiments of methodsin accordance with the invention are directed toward enhancing orotherwise inducing neuroplasticity to effectuate a particularneural-function. Neuroplasticity refers to the ability of the brain tochange or adapt over time. It was once thought adult brains becamerelatively “hard wired” such that functionally significant neuralnetworks could not change significantly over time or in response toinjury. It has become increasingly more apparent that these neuralnetworks can change and adapt over time so that meaningful function canbe regained in response to brain injury. An aspect of severalembodiments of methods in accordance with the invention is to providethe appropriate triggers for adaptive neuroplasticity. These appropriatetriggers appear to cause or enable increased synchrony of functionallysignificant populations of neurons in a network.

Electrically enhanced or induced neural stimulation in accordance withseveral embodiments of the invention excites a portion of a neuralnetwork involved in a functionally significant task such that a selectedpopulation of neurons can become more strongly associated with thatnetwork. Because such a network will subserve a functionally meaningfultask, such as motor relearning, the changes are more likely to belasting because they are continually being reinforced by natural usemechanisms. The nature of stimulation in accordance with severalembodiments of the invention ensures that the stimulated population ofneurons links to other neurons in the functional network. It is expectedthat this occurs because action potentials are not actually caused bythe stimulation, but rather are caused by interactions with otherneurons in the network. Several aspects of the electrical stimulation inaccordance with selected embodiments of the invention simply allows thisto happen with an increased probability when the network is activated byfavorable activities, such as rehabilitation or limb use.

The methods in accordance with the invention can be used to treat braindamage (e.g., stroke, trauma, etc.), brain disease (e.g., Alzheimer's,Pick's, Parkinson's, etc.), and/or brain disorders (e.g., epilepsy,depression, etc.). The methods in accordance with the invention can alsobe used to enhance functions of normal, healthy brains (e.g., learning,memory, etc.), or to control sensory functions (e.g., pain).

Certain embodiments of methods in accordance with the inventionelectrically stimulate the brain at a stimulation site whereneuroplasticity is occurring. The stimulation site may be different thanthe region in the brain where neural activity is typically present toperform the particular function according to the functional organizationof the brain. In one embodiment in which neuroplasticity related to theneural-function occurs in the brain, the method can include identifyingthe location where such neuroplasticity is present. This particularprocedure may accordingly enhance a change in the neural activity toassist the brain in performing the particular neural function. In analternative embodiment in which neuroplasticity is not occurring in thebrain, an aspect is to induce neuroplasticity at a stimulation sitewhere it is expected to occur. This particular procedure may thus inducea change in the neural activity to instigate performance of the neuralfunction. Several embodiments of these methods are expected to produce alasting effect on the intended neural activity at the stimulation site.

The specific details of certain embodiments of the invention are setforth in the following description and in FIGS. 1A-40 to provide athorough understanding of these embodiments to a person of ordinaryskill in the art. More specifically, several embodiments of methods inaccordance with the invention are initially described with reference toFIGS. 1-5C, and then several embodiments of devices for stimulating thecortical and/or deep-brain regions of the brain are described withreference to FIGS. 6-40. A person skilled in the art will understandthat the present invention may have additional embodiments, or that theinvention can be practiced without several of the details describedbelow.

A. Methods for Electrically Stimulating Regions of the Brain

1. Embodiments of Electrically Enhancing Neural Activity

FIG. 1A is a schematic representation of several neurons N1-N3 and FIG.1B is a graph illustrating an “action potential” related to neuralactivity in a normal neuron. Neural activity is governed by electricalimpulses generated in neurons. For example, neuron N1 can sendexcitatory inputs to neuron N2 (e.g., times t₁, t₃ and t₄ in FIG. 1B),and neuron N3 can send inhibitory inputs to neuron N2 (e.g., time t₂ inFIG. 1B). The neurons receive/send excitatory and inhibitory inputsfrom/to a population of other neurons. The excitatory and inhibitoryinputs can produce “action potentials” in the neurons, which areelectrical pulses that travel through neurons by changing the flux ofsodium (Na) and potassium (K) ions across the cell membrane. An actionpotential occurs when the resting membrane potential of the neuronsurpasses a threshold level. When this threshold level is reached, an“all-or-nothing” action potential is generated. For example, as shown inFIG. 1B, the excitatory input at time t₅ causes neuron N2 to “fire” anaction potential because the input exceeds the threshold level forgenerating the action potential. The action potentials propagate downthe length of the axon (the long process of the neuron that makes upnerves or neuronal tracts) to cause the release of neurotransmittersfrom that neuron that will further influence adjacent neurons.

FIG. 1C is a flowchart illustrating a method 100 for effectuating aneural-function in a patient in accordance with an embodiment of theinvention. The neural-function, for example, can control a specificmental process or physiological function, such as a particular motorfunction or sensory function (e.g., movement of a limb) that is normallyassociated with neural activity at a “normal” location in the brainaccording to the functional organization of the brain. In severalembodiments of the method 100, at least some neural activity related tothe neural-function can be occurring at a site in the brain. The site ofthe neural activity may be at the normal location where neural activitytypically occurs to carry out the neural-function according to thefunctional organization of the brain, or the site of the neural activitymay be at a different location where the brain has recruited material toperform the neural activity. In either situation, one aspect of severalembodiments of the method 100 is to determine the location in the brainwhere this neural activity is present.

The method 100 includes a diagnostic procedure 102 involving identifyinga stimulation site at a location of the brain where an intended neuralactivity related to the neural-function is present. In one embodiment,the diagnostic procedure 102 includes generating the intended neuralactivity in the brain from a “peripheral” location that is remote fromthe normal location, and then determining where the intended neuralactivity is actually present in the brain. In an alternative embodiment,the diagnostic procedure 102 can be performed by identifying astimulation site where neural activity has changed in response to achange in the neural-function. The method 100 continues with animplanting procedure 104 involving positioning first and secondelectrodes at the identified stimulation site, and a stimulatingprocedure 106 involving applying an electrical current between the firstand second electrodes. Many embodiments of the implanting procedure 104position two or more electrodes at the stimulation site, but otherembodiments of the implanting procedure involve positioning only oneelectrode at the stimulation site and another electrode remotely fromthe stimulation site. As such, the implanting procedure 104 of themethod 100 can include implanting at least one electrode at thestimulation site. The procedures 102-106 are described in greater detailbelow.

FIGS. 2-4 illustrate an embodiment of the diagnostic procedure 102. Thediagnostic procedure 102 can be used to determine the region of thebrain where stimulation will likely effectuate the desired function,such as rehabilitating a loss of a neural-function caused by a stroke,trauma, disease or other circumstance. FIG. 2, more specifically, is animage of a normal, healthy brain 200 having a first region 210 where theintended neural activity occurs to effectuate a specific neural-functionin accordance with the functional organization of the brain. Forexample, the neural activity in the first region 210 shown in FIG. 2 isgenerally associated with the movement of a patient's fingers. The firstregion 210 can have a high-intensity area 212 and a low-intensity area214 in which different levels of neural activity occur. It is notnecessary to obtain an image of the neural activity in the first region210 shown in FIG. 2 to carry out the diagnostic procedure 102, butrather it is provided to show an example of neural activity thattypically occurs at a “normal location” according to the functionalorganization of the brain 200 for a large percentage of people withnormal brain function. It will be appreciated that the actual locationof the first region 210 will generally vary between individual patients.

The neural activity in the first region 210, however, can be impaired.In a typical application, the diagnostic procedure 102 begins by takingan image of the brain 200 that is capable of detecting neural activityto determine whether the intended neural activity associated with theparticular neural function of interest is occurring at the region of thebrain 200 where it normally occurs according to the functionalorganization of the brain. FIG. 3 is an image of the brain 200 after thefirst region 210 has been affected (e.g., from a stroke, trauma or othercause). As shown in FIG. 3, the neural activity that controlled theneural-function for moving the fingers no longer occurs in the firstregion 210. The first region 210 is thus “inactive,” which is expectedto result in a corresponding loss of the movement and/or sensation inthe fingers. In some instances, the damage to the brain 200 may resultin only a partial loss of the neural activity in the damaged region. Ineither case, the image shown in FIG. 3 establishes that the loss of theneural-function is related to the diminished neural activity in thefirst region 210. The brain 200 may accordingly recruit other neurons toperform neural activity for the affected neural-function (i.e.,neuroplasticity), or the neural activity may not be present at anylocation in the brain.

FIG. 4 is an image of the brain 200 illustrating a plurality ofpotential stimulation sites 220 and 230 for effectuating theneural-function that was originally performed in the first region 210shown in FIG. 2. FIGS. 3 and 4 show an example of neuroplasticity inwhich the brain compensates for a loss of neural-function in one regionof the brain by recruiting other regions of the brain to perform neuralactivity for carrying out the affected neural-function. The diagnosticprocedure 102 utilizes the neuroplasticity that occurs in the brain toidentify the location of a stimulation site that is expected to be moreresponsive to the results of an electrical, magnetic, sonic, genetic,biologic, and/or pharmaceutical procedure to effectuate the desiredneural-function.

One embodiment of the diagnostic procedure 102 involves generating theintended neural activity remotely from the first region 210 of the brainand then detecting or sensing the location in the brain where theintended neural activity has been generated. The intended neuralactivity can be generated by applying an input that causes a signal tobe sent to the brain. For example, in the case of a patient that haslost the use of limb, the affected limb is moved and/or stimulated whilethe brain is scanned using a known imaging technique that can detectneural activity (e.g., functional MRI, positron emission tomography,etc.). In one specific embodiment, the affected limb can be moved by apractitioner or the patient, stimulated by sensory tests (e.g.,pricking), or subject to peripheral electrical stimulation. Themovement/stimulation of the affected limb produces a peripheral neuralsignal from the limb that is expected to generate a response neuralactivity in the brain. The location in the brain where this responseneural activity is present can be identified using the imagingtechnique. FIG. 4, for example, can be created by moving the affectedfingers and then noting where neural activity occurs in response to theperipheral stimulus. By peripherally generating the intended neuralactivity, this embodiment may accurately identify where the brain hasrecruited matter (i.e., sites 220 and 230) to perform the intendedneural activity associated with the neural-function.

An alternative embodiment of the diagnostic procedure 102 involvesidentifying a stimulation site at a second location of the brain wherethe neural activity has changed in response to a change in theneural-function of the patient. This embodiment of the method does notnecessarily require that the intended neural activity be generated byperipherally actuating or stimulating a body part. For example, thebrain can be scanned for neural activity associated with the impairedneural-function as a patient regains use of an affected limb or learns atask over a period of time. This embodiment, however, can also includeperipherally generating the intended neural activity remotely from thebrain explained above.

In still another embodiment, the diagnostic procedure 102 involvesidentifying a stimulation site at a location of the brain where theintended neural activity is developing to perform the neural-function.This embodiment is similar to the other embodiments of the diagnosticprocedure 102, but it can be used to identify a stimulation site at (a)the normal region of the brain where the intended neural activity isexpected to occur according to the functional organization of the brainand/or (b) a different region where the neural activity occurs becausethe brain is recruiting additional matter to perform theneural-function. This particular embodiment of the method involvesmonitoring neural activity at one or more locations where the neuralactivity occurs in response to the particular neural-function ofinterest. For example, to enhance the ability to learn a particular task(e.g., playing a musical instrument, memorizing, etc.), the neuralactivity can be monitored while a person performs the task or thinksabout performing the task. The stimulation sites can be defined by theareas of the brain where the neural activity has the highest intensity,the greatest increases, and/or other parameters that indicate areas ofthe brain that are being used to perform the particular task.

FIGS. 5A and 5B are schematic illustrations of the implanting procedure104 described above with reference to FIG. 1C for positioning the firstand second electrodes relative to a portion of the brain of a patient500. Referring to FIG. 5A, a stimulation site 502 is identified inaccordance with an embodiment of the diagnostic procedure 102. In oneembodiment, a skull section 504 is removed from the patient 500 adjacentto the stimulation site 502. The skull section 504 can be removed byboring a hole in the skull in a manner known in the art, or a muchsmaller hole can be formed in the skull using drilling techniques thatare also known in the art. In general, the hole can be 0.2-4.0 cm indiameter. Referring to FIG. 5B, an implantable stimulation apparatus 510having first and second electrodes 520 can be implanted in the patient500. Suitable techniques associated with the implantation procedure areknown to practitioners skilled in the art. After the stimulationapparatus 510 has been implanted in the patient 500, a pulse systemgenerates electrical pulses that are transmitted to the stimulation site502 by the first and second electrodes 520. Stimulation apparatussuitable for carrying out the foregoing embodiments of methods inaccordance with the invention are described in more detail below withreference to the FIGS. 6-40.

Several embodiments of methods for enhancing neural activity inaccordance with the invention are expected to provide lasting resultsthat promote the desired neural-function. Before the present invention,electrical and magnetic stimulation techniques typically stimulated thenormal locations of the brain where neural activity related to theneural-functions occurred according to the functional organization ofthe brain. Such conventional techniques, however, may not be effectivebecause the neurons in the “normal locations” of the brain may not becapable of carrying out the neural activity because of brain damage,disease, disorder, and/or because of variations of the location specificto individual patients. Several embodiments of methods for enhancingneural activity in accordance with the invention overcome this drawbackby identifying a stimulation site based on neuroplastic activity thatappears to be related to the neural-function. By first identifying alocation in the brain that is being recruited to perform the neuralactivity, it is expected that therapies (e.g., electrical, magnetic,genetic, biologic, and/or pharmaceutical) applied to this location willbe more effective than conventional techniques. This is because thelocation that the brain is recruiting for the neural activity may not bethe “normal location” where the neuro activity would normally occuraccording to the functional organization of the brain. Therefore,several embodiments of methods for enhancing neural activity inaccordance with the invention are expected to provide lasting resultsbecause the therapies are applied to the portion of the brain whereneural activity for carrying out the neural-function actually occurs inthe particular patient.

2. Electrically Inducing Desired Neural Activity

The method 100 for effectuating a neural-function can also be used toinduce neural activity in a region of the brain where such neuralactivity is not present. As opposed to the embodiments of the method 100described above for enhancing existing neural activity, the embodimentsof the method 100 for inducing neural activity initiate the neuralactivity at a stimulation site where it is estimated thatneuroplasticity will occur. In this particular situation, an image ofthe brain seeking to locate where neuroplasticity is occurring may besimilar to FIG. 3. An aspect of inducing neural activity, therefore, isto develop a procedure to determine where neuroplasticity is likely tooccur.

A stimulation site may be identified by estimating where the brain willlikely recruit neurons for performing the neural-function. In oneembodiment, the location of the stimulation site is estimated bydefining a region of the brain that is proximate to the normal locationwhere neural activity related to the neural-function is generallypresent according to the functional organization of the brain. Analternative embodiment for locating the stimulation site includesdetermining where neuroplasticity has typically occurred in patientswith similar symptoms. For example, if the brain typically recruits asecond region of the cortex to compensate for a loss of neural activityin the normal region of the cortex, then the second region of the cortexcan be selected as the stimulation site either with or without imagingthe neural activity in the brain.

Several embodiments of methods for inducing neural activity inaccordance with the invention are also expected to provide lastingresults that initiate and promote a desired neural-function. By firstestimating the location of a stimulation site where desiredneuroplasticity is expected to occur, therapies applied to this locationmay be more effective than conventional therapies for reasons that aresimilar to those explained above regarding enhancing neural activity.Additionally, methods for inducing neural activity may be easier andless expensive to implement because they do not require generatingneural activity and/or imaging the brain to determine where the intendedneural activity is occurring before applying the therapy.

3. Applications of Methods for Electrically Stimulating Regions of theBrain

The foregoing methods for enhancing existing neural activity or inducingnew neural activity are expected to be useful for many applications. Asexplained above, several embodiments of the method 100 involvedetermining an efficacious location of the brain to enhance or induce anintended neural activity that causes the desired neural-functions tooccur. Additional therapies can also be implemented in combination withthe electrical stimulation methods described above. Several specificapplications using embodiments of electrical stimulation methods inaccordance with the invention either alone or with adjunctive therapieswill now be described, but it will be appreciated that the methods inaccordance with the invention can be used in many additionalapplications.

a. General Applications

The embodiments of the electrical stimulation methods described aboveare expected to be particularly useful for rehabilitating a loss ofmental functions, motor functions and/or sensory functions caused bydamage to the brain. In a typical application, the brain has beendamaged by a stroke or trauma (e.g., automobile accident). The extent ofthe particular brain damage can be assessed using functional MRI oranother appropriate imaging technique as explained above with respect toFIG. 3. A stimulation site can then be identified by: (a) peripherallystimulating a body part that was affected by the brain damage to inducethe intended neural activity and determining the location where aresponse neural activity occurs; (b) determining where the neuralactivity has changed as a patient gains more use of the affected bodypart; and/or (c) estimating the location that the brain may recruitneurons to carry out the neural activity that was previously performedby the damaged portion of the brain. An electrical stimulation therapycan then be applied to the selected stimulation site by placing thefirst and second electrodes relative to the stimulation site to apply anelectrical current in that portion of the brain. As explained in moredetail below, it is expected that applying an electrical current to theportion of the brain that has been recruited to perform the neuralactivity related to the affected body part will produce a lastingneurological effect for rehabilitating the affected body part.

Several specific applications are expected to have a stimulation site inthe cortex because neural activity in this part of the brain effectuatesmotor functions and/or sensory functions that are typically affected bya stroke or trauma. In these applications, the electrical stimulationcan be applied directly to the pial surface of the brain or at leastproximate to the pial surface (e.g., the dura mater, the fluidsurrounding the cortex, or neurons within the cortex). Suitable devicesfor applying the electrical stimulation to the cortex are described indetail with reference to FIGS. 6-40.

The electrical stimulation methods can also be used with adjunctivetherapies to rehabilitate damaged portions of the brain. In oneembodiment, the electrical stimulation methods can be combined withphysical therapy and/or drug therapies to rehabilitate an affectedneural function. For example, if a stroke patient has lost the use of alimb, the patient can be treated by applying the electrical therapy to astimulation site where the intended neural activity is present while theaffected limb is also subject to physical therapy. An alternativeembodiment can involve applying the electrical therapy to thestimulation site and chemically treating the patient using amphetaminesor other suitable drugs.

The embodiments of the electrical stimulation methods described aboveare also expected to be useful for treating brain diseases, such asAlzheimer's, Parkinson's, and other brain diseases. In this application,the stimulation site can be identified by monitoring the neural activityusing functional MRI or other suitable imaging techniques over a periodof time to determine where the brain is recruiting material to performthe neural activity that is being affected by the disease. It may alsobe possible to identify the stimulation site by having the patient tryto perform an act that the particular disease has affected, andmonitoring the brain to determine whether any response neural activityis present in the brain. After identifying where the brain is recruitingadditional matter, the electrical stimulation can be applied to thisportion of the brain. It is expected that electrically stimulating theregions of the brain that have been recruited to perform the neuralactivity which was affected by the disease will assist the brain inoffsetting the damage caused by the disease.

The embodiments of the electrical stimulation methods described aboveare also expected to be useful for treating neurological disorders, suchas depression, passive-aggressive behavior, weight control, and otherdisorders. In these applications, the electrical stimulation can beapplied to a stimulation site in the cortex or another suitable part ofthe brain where neural activity related to the particular disorder ispresent. The embodiments of electrical stimulation methods for carryingout the particular therapy can be adapted to either increase or decreasethe particular neural activity in a manner that produces the desiredresults. For example, an amputee may feel phantom sensations associatedwith the amputated limb. This phenomenon can be treated by applying anelectrical pulse that reduces the phantom sensations. The electricaltherapy can be applied so that it will modulate the ability of theneurons in that portion of the brain to execute sensory functions.

b. Pulse Forms and Potentials

The electrical stimulation methods in accordance with the invention canuse several different pulse forms to effectuate the desiredneuroplasticity. The pulses can be a bi-phasic or monophasic stimulusthat is applied to achieve a desired potential in a sufficientpercentage of a population of neurons at the stimulation site. In oneembodiment, the pulse form has a frequency of approximately 2-1000 Hz,but the frequency may be particularly useful in the range ofapproximately 40-200 Hz. For example, initial clinical trials areexpected to use a frequency of approximately 50-100 Hz. The pulses canalso have pulse widths of approximately 10 μs-100 ms, or morespecifically the pulse width can be approximately 20-200 μs. Forexample, a pulse width of 50-100 μs may produce beneficial results.

It is expected that one particularly useful application of the inventioninvolves enhancing or inducing neuroplasticity by raising the restingmembrane potential of neurons to bring the neurons closer to thethreshold level for firing an action potential. Because the stimulationraises the resting membrane potential of the neurons, it is expectedthat these neurons are more likely to “fire” an action potential inresponse to excitatory input at a lower level.

FIG. 5C is a graph illustrating applying a subthreshold potential to theneurons N1-N3 of FIG. 1A. At times t₁ and t₂, the excitory/inhibitoryinputs from other neurons do not “bridge-the-gap” from the restingpotential at −X mV to the threshold potential. At time t₃, theelectrical stimulation is applied to the brain to raise the restingpotential of neurons in the stimulated population such that the restingpotential is at −Y mV. As such, at time t₄ when the neurons receiveanother excitatory input, even a small input exceeds the gap between theraised resting potential −Y mV and the threshold potential to induceaction potentials in these neurons. For example, if the restingpotential is approximately −70 mV and the threshold potential isapproximately −50 mV, then the electrical stimulation can be applied toraise the resting potential of a sufficient number of neurons toapproximately −52 to −60 mV.

The actual electrical potential applied to electrodes implanted in thebrain to achieve a subthreshold potential stimulation will varyaccording to the individual patient, the type of therapy, the type ofelectrodes, and other factors. In general, the pulse form of theelectrical stimulation (e.g., the frequency, pulse width, wave form, andvoltage potential) is selected to raise the resting potential in asufficient number neurons at the stimulation site to a level that isless than a threshold potential for a statistical portion of the neuronsin the population. The pulse form, for example, can be selected so thatthe applied voltage of the stimulus achieves a change in the restingpotential of approximately 10%-95%, and more specifically of 60%-80%, ofthe difference between the unstimulated resting potential and thethreshold potential.

In one specific example of a subthreshold application for treating apatient's hand, electrical stimulation is not initially applied to thestimulation site. Although physical therapy related to the patient'shand may cause some activation of a particular population of neuronsthat is known to be involved in “hand function,” only a low level ofactivation might occur because physical therapy only produces a lowlevel of action potential generation in that population of neurons.However, when the subthreshold electrical stimulation is applied, theresting membrane potentials of the neurons in the stimulated populationare elevated. These neurons now are much closer to the threshold foraction potential formation such that when the same type of physicaltherapy is given, this population of cells will have a higher level ofactivation because these cells are more likely to fire actionpotentials.

Subthreshold stimulation may produce better results than simplystimulating the neurons with sufficient energy levels to exceed thethreshold for action potential formation. One aspect of subthresholdstimulation is to increase the probability that action potentials willoccur in response to the ordinary causes of activation—such as physicaltherapy. This will allow the neurons in this functional network tobecome entrained together, or “learn” to become associated with thesetypes of activities. If neurons are given so much electricity that theycontinually fire action potentials without additional excitatory inputs(suprathreshold stimulation), this will create “noise” anddisorganization that will not likely cause improvement in function. Infact, neurons that are “overdriven” soon deplete their neurotransmittersand effectively become silent.

The application of a subthreshold stimulation is very different thansuprathreshold stimulation. Subthreshold stimulation in accordance withseveral embodiments of the invention, for example, does not intend todirectly make neurons fire action potentials with the electricalstimulation in a significant population of neurons at the stimulationsite. Instead, subthreshold stimulation attempts to decrease the“activation energy” required to activate a large portion of the neuronsat the stimulation site. As such, subthreshold stimulation in accordancewith certain embodiments of the invention is expected to increase theprobability that the neurons will fire in response to the usualintrinsic triggers, such as trying to move a limb, physical therapy, orsimply thinking about movement of a limb, etc. Moreover, coincidentstimulation associated with physical therapy is expected to increase theprobability that the action potentials that are occurring with anincreased probability due to the subthreshold stimulation will berelated to meaningful triggers, and not just “noise.”

The stimulus parameters set forth above, such as a frequency selectionof approximately 50-100 Hz and an amplitude sufficient to achieve anincrease of 60% to 80% of the difference between the resting potentialand the threshold potential are specifically selected so that they willincrease the resting membrane potential of the neurons, therebyincreasing the likelihood that they will fire action potentials, withoutdirectly causing action potentials in most of the neuron population. Inaddition, and as explained in more detail below with respect to FIGS.6-40, several embodiments of stimulation apparatus in accordance withthe invention are designed to precisely apply a pulse form that producessubthreshold stimulation by selectively stimulating regions of thecerebral cortex of approximately 1-2 cm (the estimated size of a“functional unit” of cortex), directly contacting the pial surface withthe electrodes to consistently create the same alterations in restingmembrane potential, and/or biasing the electrodes against the pialsurface to provide a positive connection between the electrodes and thecortex.

B. Devices for Electrically Stimulating Regions of the Brain

FIGS. 6-40 illustrate stimulation apparatus in accordance with severalembodiments of the invention for electrically stimulating regions of thebrain in accordance with one or more of the methods described above. Thedevices illustrated in FIGS. 6-40 are generally used to stimulate aregion of the cortex proximate to the pial surface of the brain (e.g.,the dura mater, the pia mater, the fluid between the dura mater and thepia mater, and a depth in the cortex outside of the white matter of thebrain). The devices can also be adapted for stimulating other portionsof the brain in other embodiments.

1. Implantable Stimulation Apparatus with Integrated Pulse Systems

FIG. 6 is an isometric view and FIG. 7 is a cross-sectional view of astimulation apparatus 600 in accordance with an embodiment of theinvention for stimulating a region of the cortex proximate to the pialsurface. In one embodiment, the stimulation apparatus 600 includes asupport member 610, an integrated pulse-system 630 (shown schematically)carried by the support member 610, and first and second electrodes 660(identified individually by reference numbers 660 a and 660 b). Thefirst and second electrodes 660 are electrically coupled to the pulsesystem 630. The support member 610 can be configured to be implantedinto the skull or another intracranial region of a patient. In oneembodiment, for example, the support member 610 includes a housing 612and an attachment element 614 connected to the housing 612. The housing612 can be a molded casing formed from a biocompatible material that hasan interior cavity for carrying the pulse system 630. The housing canalternatively be a biocompatible metal or another suitable material. Thehousing 612 can have a diameter of approximately 1-4 cm, and in manyapplications the housing 612 can be 1.5-2.5 cm in diameter. The housing612 can also have other shapes (e.g., rectilinear, oval, elliptical) andother surface dimensions. The stimulation apparatus 600 can weigh 35 gor less and/or occupy a volume of 20 cc or less. The attachment element614 can be a flexible cover, a rigid plate, a contoured cap, or anothersuitable element for holding the support member 610 relative to theskull or other body part of the patient. In one embodiment, theattachment element 614 is a mesh, such as a biocompatible polymericmesh, metal mesh, or other suitable woven material. The attachmentelement 614 can alternatively be a flexible sheet of Mylar, a polyester,or another suitable material.

FIG. 7, more specifically, is a cross-sectional view of the stimulationapparatus 600 after it has been implanted into a patient in accordancewith an embodiment of the invention. In this particular embodiment, thestimulation apparatus 600 is implanted into the patient by forming anopening in the scalp 702 and cutting a hole 704 through the skull 700and through the dura mater 706. The hole 704 should be sized to receivethe housing 612 of the support member 610, and in most applications, thehole 704 should be smaller than the attachment element 614. Apractitioner inserts the support member 610 into the hole 704 and thensecures the attachment element 614 to the skull 700. The attachmentelement 614 can be secured to the skull using a plurality of fasteners618 (e.g., screws, spikes, etc.) or an adhesive. In an alternativeembodiment, a plurality of downwardly depending spikes can be formedintegrally with the attachment element 614 to define anchors that can bedriven into the skull 700.

The embodiment of the stimulation apparatus 600 shown in FIG. 7 isconfigured to be implanted into a patient so that the electrodes 660contact a desired portion of the brain at the stimulation site. Thehousing 612 and the electrodes 660 can project from the attachmentelement 614 by a distance “D” such that the electrodes 660 arepositioned at least proximate to the pia mater 708 surrounding thecortex 709. The electrodes 660 can project from a housing 612 as shownin FIG. 7, or the electrodes 660 can be flush with the interior surfaceof the housing 612. In the particular embodiment shown in FIG. 7, thehousing 612 has a thickness “T” and the electrodes 660 project from thehousing 612 by a distance “P” so that the electrodes 660 press againstthe surface of the pia mater 708. The thickness of the housing 612 canbe approximately 0.5-4 cm, and is more generally about 1-2 cm. Theconfiguration of the stimulation apparatus 600 is not limited to theembodiment shown in FIGS. 6 and 7, but rather the housing 612, theattachment element 614, and the electrodes 660 can be configured toposition the electrodes in several different regions of the brain. Forexample, in an alternate embodiment, the housing 612 and the electrodes660 can be configured to position the electrodes deep within the cortex709, and/or a deep brain region 710. In general, the electrodes can beflush with the housing or extend 0.1 mm to 5 cm from the housing. Morespecific embodiments of pulse system and electrode configurations forthe stimulation apparatus will be described below.

Several embodiments of the stimulation apparatus 600 are expected to bemore effective than existing transcranial electrical stimulation devicesand transcranial magnetic stimulation devices. It will be appreciatedthat much of the power required for transcranial therapies is dissipatedin the scalp and skull before it reaches the brain. In contrast toconventional transcranial stimulation devices, the stimulation apparatus600 is implanted so that the electrodes are at least proximate to thepial surface of the brain 708. Several embodiments of methods inaccordance with the invention can use the stimulation apparatus 600 toapply an electrical therapy directly to the pia mater 708, the duramater 706, and/or another portion of the cortex 709 at significantlylower power levels than existing transcranial therapies. For example, apotential of approximately 1 mV to 10 V can be applied to the electrodes660; in many instances a potential of 100 mV to 5 V can be applied tothe electrodes 660 for selected applications. It will also beappreciated that other potentials can be applied to the electrodes 660of the stimulation apparatus 600 in accordance with other embodiments ofthe invention.

Selected embodiments of the stimulation apparatus 600 are also capableof applying stimulation to a precise stimulation site. Again, becausethe stimulation apparatus 600 positions the electrodes 660 at leastproximate to the pial surface 708, precise levels of stimulation withgood pulse shape fidelity will be accurately transmitted to thestimulation site in the brain. It will be appreciated that transcranialtherapies may not be able to apply stimulation to a precise stimulationsite because the magnetic and electrical properties of the scalp andskull may vary from one patient to another such that an identicalstimulation by the transcranial device may produce a different level ofstimulation at the neurons in each patient. Moreover, the ability tofocus the stimulation to a precise area is hindered by delivering thestimulation transcranially because the scalp, skull and dura all diffusethe energy from a transcranial device. Several embodiments of thestimulation apparatus 600 overcome this drawback because the electrodes660 are positioned under the skull 700 such that the pulses generated bythe stimulation apparatus 600 are not diffused by the scalp 702 andskull 700.

2. Integrated Pulse Systems for Implantable Stimulation Apparatus

The pulse system 630 shown in FIGS. 6 and 7 generates and/or transmitselectrical pulses to the electrodes 660 to create an electrical field ata stimulation site in a region of the brain. The particular embodimentof the pulse system 630 shown in FIG. 7 is an “integrated” unit in thatis carried by the support member 610. The pulse system 630, for example,can be housed within the housing 612 so that the electrodes 660 can beconnected directly to the pulse system 630 without having leads outsideof the stimulation apparatus 600. The distance between the electrodes660 and the pulse system 630 can be less than 4 cm, and it is generally0.10 to 2.0 cm. The stimulation apparatus 600 can accordingly provideelectrical pulses to the stimulation site without having to surgicallycreate tunnels running through the patient to connect the electrodes 660to a pulse generator implanted remotely from the stimulation apparatus600. It will be appreciated, however, that alternative embodiments ofstimulation apparatus in accordance with the invention can include apulse system implanted separately from the stimulation apparatus 600 inthe cranium or an external pulse system. Several particular embodimentsof pulse systems that are suitable for use with the stimulationapparatus 600 will now be described in more detail.

FIGS. 8 and 9 schematically illustrate an integrated pulse system 800 inaccordance with one embodiment of the invention for being implanted inthe cranium within the stimulation apparatus 600. Referring to FIG. 8,the pulse system 800 can include a power supply 810, an integratedcontroller 820, a pulse generator 830, and a pulse transmitter 840. Thepower supply 810 can be a primary battery, such as a rechargeablebattery or another suitable device for storing electrical energy. Inalternative embodiments, the power supply 810 can be an RF transducer ora magnetic transducer that receives broadcast energy emitted from anexternal power source and converts the broadcast energy into power forthe electrical components of the pulse system 800. The integratedcontroller 820 can be a wireless device that responds to command signalssent by an external controller 850. The integrated controller 820, forexample, can communicate with the external controller 850 by RF ormagnetic links 860. The integrated controller 820 provides controlsignals to the pulse generator 830 in response to the command signalssent by the external controller 850. The pulse generator 830 can have aplurality of channels that send appropriate electrical pulses to thepulse transmitter 840, which is coupled to the electrodes 660. Suitablecomponents for the power supply 810, the integrated controller 820, thepulse generator 830, and the pulse transmitter 840 are known to personsskilled in the art of implantable medical devices.

Referring to FIG. 9, the pulse system 800 can be carried by the supportmember 610 of the stimulation apparatus 600 in the manner describedabove with reference to FIGS. 6 and 7. The external controller 850 canbe located externally to the patient 500 so that the external controller850 can be used to control the pulse system 800. In one embodiment,several patients that require a common treatment can be simultaneouslytreated using a single external controller 850 by positioning thepatients within the operating proximity of the controller 850. In analternative embodiment, the external controller 850 can contain aplurality of operating codes and the integrated controller 820 for aparticular patient can have an individual operating code. A singlecontroller 850 can thus be used to treat a plurality of differentpatients by entering the appropriate operating code into the controller850 corresponding to the particular operating codes of the integratedcontrollers 820 for the patients.

FIG. 10 is a schematic view illustrating a pulse system 1000 and anexternal controller 1010 for use with the stimulation apparatus 600 inaccordance with another embodiment of the invention. In this embodiment,the external controller 1010 includes a power supply 1020, a controller1022 coupled to the power supply 1020, and a user interface 1024 coupledto the controller 1022. The external controller 1010 can also include apulse generator 1030 coupled to the power supply 1020, a pulsetransmitter 1040 coupled to the pulse generator 1030, and an antenna1042 coupled to the pulse transmitter 1040. The external controller 1010generates the power and the pulse signal, and the antenna 1042 transmitsa pulse signal 1044 to the pulse system 1000 in the stimulationapparatus 600. The pulse system 1000 receives the pulse signal 1044 anddelivers an electrical pulse to the electrodes. The pulse system 1000,therefore, does not necessarily include an integrated power supply,controller and pulse generator within the housing 610 because thesecomponents are in the external controller 1010.

FIG. 11 is a schematic view illustrating an embodiment of the pulsesystem 1000 in greater detail. In this embodiment, the pulse system 1000is carried by the support member 610 of the stimulation apparatus 600.The pulse system 1000 can include an antenna 1060 and a pulse deliverysystem 1070 coupled to the antenna 1060. The antenna 1060 receives thepulse signal 1044 from the external controller 1010 and sends the pulsesignal 1044 to the pulse delivery system 1070, which transforms thepulse signal 1044 into electrical pulses. Accordingly, the electrodes660 can be coupled to the pulse delivery system 1070. The pulse deliverysystem 1070 can include a filter to remove noise from the pulse signal1044 and a pulse former that creates an electrical pulse from the pulsesignal 1044. The pulse former can be driven by the energy in the pulsesignal 1044, or in an alternative embodiment, the pulse system 1000 canalso include an integrated power supply to drive the pulse former.

FIG. 12 is a schematic view illustrating an embodiment of pulse system1200 for use in an embodiment of the stimulation apparatus 600, and anexternal controller 1210 for controlling the pulse system 1200 remotelyfrom the patient using RF energy. In this embodiment, the externalcontroller 1210 includes a power supply 1220, a controller 1222 coupledto the power supply 1220, and a pulse generator 1230 coupled to thecontroller 1222. The external controller 1210 can also include amodulator 1232 coupled to the pulse generator 1230 and an RF generator1234 coupled to the modulator 1232. In operation, the externalcontroller 1210 broadcasts pulses of RF energy via an antenna 1242.

The pulse system 1200 can be housed within the stimulation apparatus 600(not shown). In one embodiment, the pulse system 1200 includes anantenna 1260 and a pulse delivery system 1270. The antenna 1260incorporates a diode (not shown) that rectifies the broadcast RF energyfrom the antenna 1242. The pulse delivery system 1270 can include afilter 1272 and a pulse former 1274 that forms electrical pulses whichcorrespond to the RF energy broadcast from the antenna 1242. The pulsesystem 1200 is accordingly powered by the RF energy in the pulse signalfrom the external controller 1210 such that the pulse system 1200 doesnot need a separate power supply carried by the stimulation apparatus600.

FIG. 13 is a cross-sectional view of a pulse system 1300 for use inanother embodiment of the implantable stimulation apparatus 600,together with an external controller 1310 for remotely controlling thepulse system 1300 externally from the patient using magnetic energy. Inthis embodiment, the external controller 1310 includes a power supply1320, a controller 1322 coupled to the power supply 1320, and a userinterface 1324 coupled to the controller 1322. The external controller1310 can also include a pulse generator 1330 coupled to the controller1332, a pulse transmitter 1340 coupled to the pulse generator 1330, anda magnetic coupler 1350 coupled to the pulse transmitter 1340. Themagnetic coupler 1350 can include a ferrite core 1352 and a coil 1354wrapped around a portion of the ferrite core 1352. The coil 1354 canalso be electrically connected to the pulse transmitter 1340 so thatelectrical pulses applied to the coil 1354 generate changes in acorresponding magnetic field. The magnetic coupler 1350 can also includea flexible cap 1356 to position the magnetic coupler 1350 over theimplanted stimulation apparatus 600.

The pulse system 1300 can include a ferrite core 1360 and a coil 1362wrapped around a portion of the ferrite core 1360. The pulse system 1310can also include a pulse delivery system 1370 including a rectifier anda pulse former. In operation, the ferrite core 1360 and the coil 1362convert the changes in the magnetic field generated by the magneticcoupler 1350 into electrical pulses that are sent to the pulse deliverysystem 1370. The electrodes 660 are coupled to the pulse delivery system1370 so that electrical pulses corresponding to the electrical pulsesgenerated by the pulse generator 1330 in the external controller 1310are delivered to the stimulation site on the patient.

3. Electrode Configurations

FIGS. 14-24 illustrate electrodes in accordance with various embodimentsof the invention that can be used with the stimulation apparatusdisclosed herein. FIGS. 14-22 illustrate embodiments of electrodesconfigured to apply an electrical current to a stimulation site at leastproximate to the pial surface of the cortex, and FIGS. 23 and 24illustrate embodiments of electrodes configured to apply an electricalcurrent within the cortex or below the cortex. It will be appreciatedthat other configurations of electrodes can also be used with otherimplantable stimulation apparatus.

FIG. 14 is a bottom plan view and FIG. 15 is a cross-sectional view of astimulation apparatus 1400 in accordance with an embodiment of theinvention. In this embodiment, the stimulation apparatus 1400 includes afirst electrode 1410 and a second electrode 1420 concentricallysurrounding the first electrode 1410. The first electrode 1410 can becoupled to the positive terminal of a pulse generator 1430, and thesecond electrode 1420 can be coupled to the negative terminal of thepulse generator 1430. Referring to FIG. 15, the first and secondelectrodes 1410 and 1420 generate a toroidal electric field 1440.

FIG. 16 is a bottom plan view and FIG. 17 is a cross-sectional view of astimulation apparatus 1600 in accordance with another embodiment of theinvention. In this embodiment, the stimulation apparatus 1600 includes afirst electrode 1610, a second electrode 1620 surrounding the firstelectrode 1610, and a third electrode 1630 surrounding the secondelectrode 1620. The first electrode 1610 can be coupled to the negativeterminals of a first pulse generator 1640 and a second pulse generator1642; the second electrode 1620 can be coupled to the positive terminalof the first pulse generator 1640; and the third electrode 1630 can becoupled to the positive terminal of the second pulse generator 1642. Inoperation, the first electrode 1610 and the third electrode 1630generate a first toroidal electric field 1650, and the first electrodethe 1610 and the second electrode 1620 generate a second toroidalelectric field 1660. The second toroidal electric field 1660 can bemanipulated to vary the depth that the first toroidal electric field1650 projects away from the base of the stimulation apparatus 1600.

FIG. 18 is a bottom plan view and FIG. 19 is a cross-sectional view of astimulation apparatus 1800 in accordance with yet another embodiment ofthe invention. In this embodiment, the stimulation apparatus 1800includes a first electrode 1810 and a second electrode 1820 spaced apartfrom the first electrode 1810. The first and second electrodes 1810 and1820 are linear electrodes which are coupled to opposite terminals of apulse generator 1830. Referring to FIG. 19, the first and secondelectrodes 1810 and 1820 can generate an approximately linear electricfield.

FIG. 20 is a bottom plan view of a stimulation apparatus 2000 inaccordance with still another embodiment of the invention. In thisembodiment, the stimulation apparatus 2000 includes a first electrode2010, a second electrode 2020, a third electrode 2030, and a fourthelectrode 2040. The first and second electrodes 2010 and 2020 arecoupled to a first pulse generator 2050, and the third and fourthelectrodes 2030 and 2040 are coupled to a second pulse generator 2060.More specifically, the first electrode 2010 is coupled to the positiveterminal and the second electrode 2020 is coupled to the negativeterminal of the first pulse generator 2050, and the third electrode 2030is coupled to the positive terminal and the fourth electrode 2040 iscoupled to the negative terminal of the second pulse generator 2060. Thefirst and second electrodes 2010 and 2020 are expected to generate afirst electric field 2070, and the third and fourth electrodes 2030 and2040 are expected to generate a second electric field 2072. It will beappreciated that the ions will be relatively free to move through thebrain such that a number of ions will cross between the first and secondelectric fields 2070 and 2072 as shown by arrows 2074. This embodimentprovides control of electric field gradients at the stimulation sites.

FIG. 21 is a bottom plan view of another embodiment of the stimulationapparatus 2000. In this embodiment, the first electrode 2010 is coupledto the positive terminal and the second electrode 2020 is coupled to thenegative terminal of the first pulse generator 2050. In contrast to theembodiment shown in FIG. 20, the third electrode 2030 is coupled to thenegative terminal and the fourth electrode 2040 is coupled to thepositive terminal of the second pulse generator 2070. It is expectedthat this electrode arrangement will result in a plurality of electricfields between the electrodes. This allows control of the direction ororientation of the electric field.

FIG. 22 is a bottom plan view that schematically illustrates astimulation apparatus 2200 in accordance with still another embodimentof the invention. In this embodiment, the stimulation apparatus 2200includes a first electrode 2210, a second electrode 2220, a thirdelectrode 2230, and a fourth electrode 2240. The electrodes are coupledto a pulse generator 2242 by a switch circuit 2250. The switch circuit2250 can include a first switch 2252 coupled to the first electrode2210, a second switch 2254 coupled to the second electrode 2220, a thirdswitch 2256 coupled to the third electrode 2230, and a fourth switch2258 coupled to the fourth electrode 2240. In operation, the switches2252-2258 can be opened and closed to establish various electric fieldsbetween the electrodes 2210-2240. For example, the first switch 2252 andthe fourth switch 2258 can be closed in coordination with a pulse fromthe pulse generator 2242 to generate a first electric field 2260, and/orthe second switch 2254 and the third switch 2256 can be closed incoordination with another pulse from the pulse generator 2242 togenerate a second electric field 2270. The first and second electricfields 2260 and 2270 can be generated at the same pulse to produceconcurrent fields or alternating pulses to produce alternating orrotating fields.

FIG. 23 is a bottom plan view and FIG. 24 is a side elevational view ofa stimulation apparatus 2300 in accordance with another embodiment ofthe invention. In this embodiment, the stimulation apparatus 2300 has afirst electrode 2310, a second electrode 2320, a third electrode 2330,and a fourth electrode 2340. The electrodes 2310-2340 can be configuredin any of the arrangements set forth above with reference to FIGS.14-22. The electrodes 2310-2340 also include electrically conductivepins 2350 and/or 2360. The pins 2350 and 2360 can be configured toextend below the pial surface of the cortex. For example, because thelength of the pin 2350 is less than the thickness of the cortex 709, thetip of the pin 2350 will accordingly conduct the electrical pulses to astimulation site within the cortex 709 below the pial surface. Thelength of the pin 2360 is greater than the thickness of the cortex 709to conduct the electrical pulses to a portion of the brain below thecortex 709, such as a deep brain region 710. The lengths of the pins areselected to conduct the electrical pulses to stimulation sites below thepia mater 708. As such, the length of the pins 2350 and 2360 can be thesame for each electrode or different for individual electrodes.Additionally, only a selected portion of the electrodes and the pins canhave an exposed conductive area. For example, the electrodes 2310-2340and a portion of the pins 2350 and 2360 can be covered with a dielectricmaterial so that only exposed conductive material is at the tips of thepins. It will also be appreciated that the configurations of electrodesset forth in FIGS. 14-22 can be adapted to apply an electrical currentto stimulation sites below the pia mater by providing pin-likeelectrodes in a matter similar to the electrodes shown in FIGS. 23 and24.

Several embodiments of the stimulation apparatus described above withreference to FIGS. 6-24 are expected to be more effective than existingtranscranial or subcranial stimulation devices. In addition topositioning the electrodes under the skull, many embodiments of thestimulation apparatus described above also accurately focus theelectrical energy in desired patterns relative to the pia mater 708, thedura mater 706, and/or the cortex 709. It will be appreciated thattranscranial devices may not accurately focus the energy because theelectrodes or other types of energy emitters are positioned relativelyfar from the stimulation sites and the skull diffuses some of theenergy. Also, existing subcranial devices generally merely place theelectrodes proximate to a specific nerve, but they do not provideelectrode configurations that generate an electrical field in a patterndesigned for the stimulation site. Several of the embodiments of thestimulation apparatus described above with reference to FIGS. 6-24overcome this drawback because the electrodes can be placed against theneurons at the desired stimulation site. Additionally, the electrodeconfigurations of the stimulation apparatus can be configured to providea desired electric field that is not diffused by the skull 700.Therefore, several embodiments of the stimulation apparatus inaccordance with the invention are expected to be more effective becausethey can accurately focus the energy at the stimulation site.

4. Implantable Stimulation Apparatus with Biasing Elements

FIGS. 25-30 illustrate several embodiments of stimulation apparatushaving a biasing element in accordance with a different aspect of theinvention. The stimulation apparatus shown in FIGS. 25-30 can be similarto those described above with reference to FIGS. 6-24. Therefore, theembodiments of the stimulation apparatus shown in FIGS. 25-30 can havethe same pulse systems, support members and electrode configurationsdescribed is above with reference to FIGS. 6-24

FIG. 25 is an isometric view and FIG. 26 is a cross-sectional view of astimulation apparatus 2500 in accordance with an embodiment of theinvention. In one embodiment, the stimulation apparatus 2500 includes asupport member 2510, a pulse-system 2530 carried by the support member2510, and first and second electrodes 2560 coupled to the pulse system2530. The support member 2510 can be identical or similar to the supportmember 610 described above with reference to FIGS. 6 and 7. The supportmember 2510 can accordingly include a housing 2512 configured to beimplanted in the skull 700 and an attachment element 2514 configured tobe connected to the skull 700 by fasteners 2518 (FIG. 2), an adhesive,and/or an anchor. The pulse system 2530 can be identical or similar toany of the pulse systems described above with reference to FIGS. 6-13,and the first and second electrodes 2560 can have any of the electrodeconfigurations explained above with reference to FIGS. 14-24. Unlike thestimulation apparatus described above, however, the stimulationapparatus 2500 includes a biasing element 2550 coupled to the electrodes2560 to mechanically bias the electrodes 2560 away from the supportmember 2510. In an alternative embodiment, the biasing element 2550 canbe positioned between the housing 2512 and the attachment element 2514,and the electrodes 2560 can be attached directly to the housing 2512. Asexplained in more detail below, the biasing element 2550 can be acompressible member, a fluid filled bladder, a spring, or any othersuitable element that resiliently and/or elastically drives theelectrodes 2560 away from the support member 2510.

FIG. 26 illustrates an embodiment of the stimulation apparatus 2500after it has been implanted into the skull 700 of a patient. When thefasteners 2518 are attached to the skull 700, the biasing element 2550should be compressed slightly so that the electrodes 2560 contact thestimulation site. In the embodiment shown in FIG. 26, the compressedbiasing element 2550 gently presses the electrodes 2560 against thesurface of the pia mater 708. It is expected that the biasing element2550 will provide a uniform, consistent contact between the electrodes2560 and the pial surface of the cortex 709. The stimulation apparatus2500 is expected to be particularly useful when the implantable deviceis attached to the skull and the stimulation site is on the pia mater708 or the dura mater 706. It can be difficult to position the contactsagainst the pia mater 708 because the distance between the skull 700,the dura mater 706, and the pia mater 708 varies within the cranium asthe brain moves relative to the skull, and also as the depth varies fromone patient to another. The stimulation apparatus 2500 with the biasingelement 2550 compensates for the different distances between the skull700 and the pia mater 708 so that a single type of device can inherentlyfit several different patients. Moreover, the stimulation apparatus 2500with the biasing element 2550 adapts to changes as the brain moveswithin the skull. In contrast to the stimulation apparatus 2500 with thebiasing element 2550, an implantable device that does not have a biasingelement 2550 may not fit a particular patient or may not consistentlyprovide electrical contact to the pia mater.

FIGS. 27 and 28 are cross-sectional views of stimulation apparatus inwhich the biasing elements are compressible members. FIG. 27, morespecifically, illustrates a stimulation apparatus 2700 having a biasingelement 2750 in accordance with an embodiment of the invention. Thestimulation apparatus 2700 can have an integrated pulse system 2530 andelectrodes 2560 coupled to the pulse system 2530 in a manner similar tothe stimulation apparatus 2500. The biasing element 2750 in thisembodiment is a compressible foam, such as a biocompatible closed cellfoam or open cell foam. As best shown in FIG. 27, the biasing element2750 compresses when the stimulation apparatus 2700 is attached to theskull. FIG. 28 illustrates a stimulation apparatus 2800 having a biasingelement 2850 in accordance with another embodiment of the invention. Thebiasing element 2850 can be a compressible solid, such as silicon rubberor other suitable compressible materials. The electrodes 2560 areattached to the biasing element 2850.

FIG. 29 is a cross-sectional view of a stimulation apparatus 2900 havinga biasing element 2950 in accordance with another embodiment of theinvention. The stimulation apparatus 2900 can have a support member 2910including an internal passageway 2912 and a diaphragm 2914. The biasingelement 2950 can include a flexible bladder 2952 attached to the supportmember 2910, and the electrodes 2560 can be attached to the flexiblebladder 2952. In operation, the flexible bladder 2952 is filled with afluid 2954 until the electrodes 2560 press against the stimulation site.In one embodiment, the flexible bladder 2952 is filled by inserting aneedle of a syringe 2956 through the diaphragm 2914 and injecting thefluid 2954 into the internal passageway 2912 and the flexible bladder.

FIG. 30 is a cross-sectional view of a stimulation apparatus 3000 havinga biasing element 3050 in accordance with another embodiment of theinvention. In this embodiment, the biasing element 3050 is a spring andthe electrodes 2560 are attached to the spring. The biasing element 3050can be a wave spring, a leaf spring, or any other suitable spring thatcan mechanically bias the electrodes 2560 against the stimulation site.

Although several embodiments of the stimulation apparatus shown in FIGS.25-30 can have a biasing element and any of the pulse systems set forthabove with respect to FIGS. 6-13, it is not necessary to have a pulsesystem contained within the support member. Therefore, certainembodiments of implantable stimulation apparatus in accordance with theinvention can have a pulse system and/or a biasing member in anycombination of the embodiments set forth above with respect to FIGS.6-30.

5. Implantable Stimulation Apparatus with External Pulse Systems

FIGS. 31-35 are schematic cross-sectional views of various embodimentsof implantable stimulation apparatus having external pulse systems. FIG.31, more specifically, illustrates an embodiment of a stimulationapparatus 3100 having a biasing element 3150 to which a plurality ofelectrodes 3160 are attached in a manner similar to the stimulationapparatus described above with reference to FIGS. 25-30. It will beappreciated that the stimulation apparatus 3100 may not include thebiasing element 3150. The stimulation apparatus 3100 can also include anexternal receptacle 3120 having an electrical socket 3122 and animplanted lead line 3124 coupling the electrodes 3160 to contacts (notshown) in the socket 3122. The lead line 3124 can be implanted in asubcutaneous tunnel or other passageway in a manner known to a personskilled and art.

The stimulation apparatus 3100, however, does not have an internal pulsesystem carried by the portion of the device that is implanted in theskull 700 of the patient 500. The stimulation apparatus 3100 receiveselectrical pulses from an external pulse system 3130. The external pulsesystem 3130 can have an electrical connector 3132 with a plurality ofcontacts 3134 configured to engage the contacts within the receptacle3120. The external pulse system 3130 can also have a power supply,controller, pulse generator, and pulse transmitter to generate theelectrical pulses. In operation, the external pulse system 3130 sendselectrical pulses to the stimulation apparatus 3100 via the connector3132, the receptacle 3120, and the lead line 3124.

FIGS. 32 and 33 illustrate an embodiment of a stimulation apparatus 3200for use with an external pulse system in accordance with anotherembodiment of the invention. Referring to FIG. 33, the stimulationapparatus 3200 can include a support structure 3210 having a socket3212, a plurality of contacts 3214 arranged in the socket 3212, and adiaphragm 3216 covering the socket 3212. The stimulation apparatus 3200can also include a biasing element 3250 and a plurality of electrodes3260 attached to the biasing element 3250. Each electrode 3260 isdirectly coupled to one of the contacts 3214 within the supportstructure 3210. It will be appreciated that an alternative embodiment ofthe stimulation apparatus 3200 does not include the biasing element3250.

Referring to FIGS. 32 and 33 together, the stimulation apparatus 3200receives the electrical pulses from an external pulse system 3230 thathas a power supply, controller, pulse generator, and pulse transmitter.The external pulse system 3230 can also include a plug 3232 having aneedle 3233 (FIG. 33) and a plurality of contacts 3234 (FIG. 33)arranged on the needle 3233 to contact the internal contacts 3214 in thesocket 3212. In operation, the needle 3233 is inserted into the socket3212 to engage the contacts 3234 with the contacts 3214, and then thepulse system 3230 is activated to transmit electrical pulses to theelectrodes 3260.

FIGS. 34 and 35 illustrate additional embodiments of stimulationapparatus for use with external pulse systems. FIG. 34 illustrates anembodiment of a stimulation apparatus 3400 having electrodes 3410coupled to a lead line 3420 that extends under the scalp 702 of thepatient 500. The lead line 3420 is coupled to an external pulse system3450. FIG. 35 illustrates an embodiment of a stimulation apparatus 3500having a support member 3510, electrodes 3512 coupled to the supportmember 3510, and an external receptacle 3520 mounted on the scalp 702.The external receptacle 3520 can also be connected to the support member3510. The external receptacle 3520 can have a socket 3522 with contacts(not shown) electrically coupled to the electrodes 3512. The stimulationapparatus 3500 can be used with the external pulse system 3130 describedabove with reference to FIG. 31 by inserting the plug 3132 into thesocket 3522 until the contacts 3134 on the plug 3132 engage the contactswithin the socket 3522.

6. Alternate Embodiments of Implantable Stimulation Apparatus

FIG. 36 is a schematic cross-sectional view of an implantablestimulation apparatus 3600 in accordance with another embodiment of theinvention. In one embodiment, the stimulation apparatus 3600 has asupport structure 3610 and a plurality of electrodes 3620 coupled to thesupport structure 3610. The support structure 3610 can be configured tobe implanted under the skull 700 between an interior surface 701 of theskull 700 and the pial surface of the brain. The support structure 3610can be a flexible or compressible body such that the electrodes 3620contact the pia mater 708 when the stimulation apparatus 3600 isimplanted under the skull 700. In other embodiments, the supportstructure 3610 can position the electrodes 3620 so that they areproximate to, but not touching, the pia mater 708.

In one embodiment, the stimulation apparatus 3600 can receive electricalpulses from an external controller 3630. For example, the externalcontroller 3630 can be electrically coupled to the stimulation apparatus3600 by a lead line 3632 that passes through a hole 711 in the skull700. In an alternative embodiment, the stimulation apparatus 3600 caninclude an integrated pulse system similar to the pulse systemsdescribed above with reference to FIGS. 6-13. Such an embodiment of thestimulation apparatus 3600 can accordingly use a wireless externalcontrol unit. It will be appreciated that the electrodes 3620 of thestimulation apparatus 3600 can have several of the electrodeconfigurations described above with reference to FIGS. 14-24.

FIGS. 37 and 38 illustrate one embodiment of the implantable stimulationapparatus 3600. Referring to FIG. 37, the support structure 3610 can bea flexible substrate and the electrodes 3620 can be conductive elementsthat are printed onto the flexible substrate. The stimulation apparatus3600, for example, can be manufactured in a manner similar to flexibleprinted circuit assemblies that are used in electrical components. Thestimulation apparatus 3600 can be implanted under the skull 700 using aninsertion tool 3700. In one embodiment, the insertion tool 3700 has ahandle 3702 and a shaft 3704 projecting from the handle 3702. The shaft3704 can have a slot 3706 configured to receive a flat portion of thesupport member 3610. Referring to FIG. 38, the support member 3610 iswrapped around the shaft 3704, and then the stimulation apparatus 3600is passed to a tube 3720 positioned in the hole 711 through the scalp700 and the dura mater 706. After the stimulation apparatus 3600 hasbeen passed through the tube 3720, it is unfurled to place the iselectrodes 3620 at least proximate to the pia mater 708. The electrodes3620 can be coupled to an external controller by the lead lines 3632.

FIG. 39 illustrates another embodiment of an implantable stimulationapparatus 3900 that is also configured to be positioned between theskull 700 and the pia mater 708. In one embodiment, the stimulationapparatus 3900 can include a support member 3910 and a plurality ofelectrodes 3920 coupled to the support member 3910. The electrodes 3920can be coupled to individual lead lines 3922 to connect the electrodes3920 to an external pulse system. In an alternative embodiment, anintegrated pulse system 3930 can be carried by the support member 3910so that the electrodes 3920 can be coupled directly to the integratedpulse system 3930 without external lead lines 3922. The support member3910 can be a resiliently compressible member, an inflatableballoon-like device, or a substantially solid incompressible body. Inthe particular embodiment shown in FIG. 39, the support member 3910 isan inflatable balloon-like device that carries the electrodes 3920. Inoperation, the stimulation apparatus 3900 is implanted by passing thedistal end of the support member 3910 through the hole 711 in the skull700 until the electrodes 3920 are positioned at a desired stimulationsite.

FIG. 40 is a schematic illustration of a stimulation apparatus 4000together with an internal pulse system 4030 in accordance with anotherembodiment of the invention. The stimulation apparatus 4000 can includea support member 4010, a biasing element 4015 carried by the supportmember 4010, and a plurality of electrodes 4020 carried by the biasingelement 4015. The internal pulse system 4030 can be similar to any ofthe integrated pulse systems described above with reference to FIGS.6-13, but the internal pulse system 4030 is not an integrated pulsesystem because it is not carried by the housing 4010. The internal pulsesystem 4030 can be coupled to the electrodes 4020 by a cable 4034. In atypical application, the cable 4034 is implanted subcutaneously in atunnel from a subclavicular region, along the back of the neck, andaround the skull. The stimulation apparatus 4000 can also include any ofthe electrode configurations described above with reference to FIGS.14-24.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thespirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1-123. (canceled)
 124. A method of stimulating the brain of a patient,comprising: selecting a stimulation site at the cortex of the brain ofthe patient; implanting an electrode under the skull of the patient atthe stimulation site; determining a threshold for the individual patientat which an electrical signal delivered via the implanted electrodedirectly triggers a neural reaction in response to the signal; andapplying electrical stimulation directly to the stimulation site via theimplanted electrode at a level less than the determined threshold. 125.The method of claim 124 wherein determining the threshold comprisesapplying an electrical signal to the stimulation site via the electrodeat a level that causes neurons to fire action potentials withoutadditional intrinsic input.
 126. The method of claim 124 whereinselecting a stimulation site comprises obtaining signals correspondingto neural function of the brain of the patient and determining where achange in an intrinsic, patient-specific neural-activity is suspected ofoccurring to carry out a particular physical and/or cognitive functionof the patient.
 127. The method of claim 126 wherein the stimulationsite is selected to recover functionality damaged by a brain injury, andwherein the method further comprises performing physical therapyassociated with the damaged functionality while applying the electricalstimulation to the stimulation site.
 128. The method of claim 124wherein selecting the stimulation site comprises identifying a locationof the cortex where neural-activity associated with a particularfunction damaged by a stroke is expected to occur, and wherein themethod further comprises performing physical therapy associated with theparticular function while applying the electrical stimulation.
 129. Themethod of claim 124 wherein implanting the electrode comprisespositioning a surface electrode under the skull at the dura.
 130. Themethod of claim 124 wherein: the electrode comprises an elongated memberhaving a stimulation portion; implanting the electrode comprisespositioning the stimulation portion of the elongated member within thecortex; and applying the electrical stimulation comprises delivering theelectrical stimulation from the stimulation portion of the elongatedmember within the cortex.
 131. A method of stimulating the brain of apatient, comprising: selecting a stimulation site at the cortex of thebrain of the patient; implanting an electrode under the skull of thepatient at the stimulation site; and applying electrical stimulationdirectly to the cortex, wherein the electrical stimulation decreasesactivation energy such that neurons at the stimulation site fire actionpotentials in response to intrinsic neural triggers, and wherein theelectrical stimulation is below a threshold for the individual patientat which the electrical stimulation directly causes the neurons to firethe action potentials.
 132. The method of claim 131, further comprisingdetermining the threshold at which the electrical stimulation directlytriggers causes the neurons to fire action potentials.
 133. The methodof claim 131 wherein the stimulation site is selected to recoverfunctionality damaged by a brain injury, and wherein the method furthercomprises performing physical therapy associated with the damagedfunctionality while applying the electrical stimulation to thestimulation site.
 134. The method of claim 131 wherein selecting thestimulation site comprises identifying a location of the cortex whereneural-activity associated with a particular function damaged by astroke is expected to occur, and wherein the method further comprisesperforming physical therapy associated with the particular functionwhile applying the electrical stimulation.
 135. The method of claim 131wherein implanting the electrode comprises positioning a surfaceelectrode under the skull at the dura.
 136. The method of claim 131wherein implanting the electrode comprises positioning a pin electrodehaving a stimulation portion such that the stimulation portion is withinthe cortex, and wherein the pin has a length less than an extent of thecortex at the stimulation site such that the electrical stimulation isdelivered from the stimulation portion within the cortex.
 137. A methodfor stimulating the brain of a patient, comprising: selecting astimulation site at the cortex of the brain of the patient; determininga threshold for the individual patient at which an electrical signaldirectly causes a reaction in neurons in response to the signal;implanting an electrode under the skull of the patient at thestimulation site; and applying electrical stimulation directly to thestimulation site via the implanted electrode at a level less than thedetermined threshold.
 138. The method of claim 137 wherein determiningthe threshold comprises applying an electrical signal to the stimulationsite via the electrode at a level that causes neurons to fire actionpotentials without additional intrinsic input.
 139. The method of claim137 wherein selecting a stimulation site comprises obtaining signals ofneural activity of the brain of the patient and determining where achange in an intrinsic, patient-specific neural-activity is suspected ofoccurring to carry out a particular physical and/or cognitive functionof the patient.
 140. The method of claim 139 wherein the stimulationsite is selected to recover functionality damaged by a stroke, andwherein the method further comprises performing physical therapyassociated with the damaged functionality while applying the electricalstimulation to the stimulation site.
 141. The method of claim 137wherein selecting the stimulation site comprises identifying a locationof the cortex where neural-activity associated with a particularfunction damaged by a brain injury is expected to occur, and wherein themethod further comprises performing physical therapy associated with theparticular function while applying the electrical stimulation.
 142. Themethod of claim 137 wherein implanting the electrode comprisespositioning a surface electrode under the skull at the dura.
 143. Themethod of claim 137 wherein implanting the electrode comprisespositioning an elongated member having a stimulation portion through apial surface of the cortex, and wherein the stimulation portion of theelongated member is within the cortex at the stimulation site such thatthe electrical stimulation is delivered from within the cortex and belowthe pial surface.
 144. The method of claim 137 wherein the patient hasbeen diagnosed with depression and the stimulation site is selected totreat depression.
 145. A method of stimulating the brain of a patient,comprising: selecting a stimulation site at the cortex of the brain ofthe patient; implanting an electrode under the skull of the patient atthe stimulation site; estimating a threshold for the individual patientat which an electrical signal delivered via the implanted electrodedirectly triggers a neural reaction in response to the signal; andapplying electrical stimulation directly to the stimulation site via theimplanted electrode at a level less than approximately 80% of theestimated threshold.
 146. The method of claim 145 wherein the electricalstimulation is applied at a level less than approximately 60% of theestimated threshold.
 147. The method of claim 145 wherein the electricalstimulation is at a level of approximately 50% of the estimatedthreshold.
 148. The method of claim 145 wherein estimating the thresholdcomprises applying an electrical signal to the stimulation site via theelectrode at a level that causes neurons to fire action potentialswithout additional intrinsic input.
 149. The method of claim 148 whereinthe electrical stimulation is applied at a level less than approximately60% of the determined threshold.
 150. The method of claim 148 whereinthe electrical stimulation is applied at a level of approximately 50% ofthe determined threshold.
 151. The method of claim 145 wherein: theelectrode comprises a base configured to contact a dura layer at thecortex and a pin projecting from the base; implanting the electrodeunder the skull comprises positioning the pin within the cortex; andapplying the electrical stimulation comprises delivering the electricalstimulation from within the cortex.
 152. The method of claim 145wherein: the electrode comprises an elongated member having astimulation portion; implanting the electrode comprises positioning thestimulation portion within the cortex under a pial layer; and applyingthe electrical stimulation comprises delivering an electrical signalfrom the stimulation portion of the elongated member.